[Explanation for Conventional Art]
A high-pixel and high frame-rate imaging element may be employed as an imaging device for product inspection.
On the other hand, an output interface of an imaging device used for FA (Factory Automation) includes USB3.0, Gigabit Ethernet (“Ethernet” is registered trademark), CameraLink, and the like, but has limitations from the viewpoint of an amount of data that can be transmitted per a unit time due to band limiting and thus has a small amount of transmission data compared to an amount of output data of an imaging element.
Data conversion can be performed from a high frame rate (imaging frame rate) of an imaging element to a low frame rate (transmission frame rate) of an output interface by thinning out frames from the imaging element. However, because the thinned-out frames are not transmitted, this method is unsuitable for product inspection.
A conventional imaging device, which writes the predetermined number of frames required for inspection into a memory at a high imaging frame rate and reads the frames at a low transmission frame rate, enables data transmission without dropping images (frame dropping). However, the conventional imaging device cannot perform the inspection on the next product until the set number of images are read.
[Conventional Imaging Device: FIG. 6]
The configuration of a conventional imaging device will be explained with reference to FIG. 6. FIG. 6 is a block diagram illustrating the configuration of the conventional imaging device.
As illustrated in FIG. 6, the conventional imaging device includes an imaging element 11, a serial-parallel conversion unit 12, a memory unit 13, a video signal processing unit 14, an interface output processing unit 15, and a control unit 16.
The imaging element 11 converts electric charges generated in accordance with incident light into digital data and outputs the digital data at a high imaging frame rate.
The serial-parallel conversion unit 12 converts serial data input from the imaging element 11 into parallel data and writes the parallel data into the memory unit 13.
The memory unit 13 stores therein the written image data by the predetermined number of images (frames).
The video signal processing unit 14 performs signal processing required for transmission.
The interface output processing unit 15 outputs the image data at a predetermined transmission frame rate.
The control unit 16 controls each component of the imaging device based on setting from the outside and outputs timing signals to each component to make each component perform the imaging of an object and the output of video.
Moreover, the imaging device is connected to an inspection device that performs inspection based on the captured images and an object moving apparatus that moves a product (board etc.) as an object. When an imaging start signal is input from the external object moving apparatus, the control unit 16 instructs the imaging element 11 to start to capture this object.
Then, the image data captured by the imaging device is transmitted to, for example, the inspection device from the interface output processing unit 15 to be determined as to whether the product is good or bad.
[Control Timing of Conventional Imaging Device: FIG. 7]
Next, control timing of the conventional imaging device will be explained with reference to FIG. 7. FIG. 7 is a timing diagram illustrating control timing in the conventional imaging device.
First, as illustrated in FIG. 7(a), when an imaging start signal is input from the outside (object moving apparatus), the control unit 16 outputs an exposure period signal to the imaging element 11 as illustrated in FIG. 7(b). Herein, it is assumed that 50 frames per one object are captured.
The exposure period signal is a signal for providing the timings of the start and end of exposure and the output start of data to the imaging element 11.
In other words, the imaging element 11 starts exposure when the exposure period signal becomes a high level. When the exposure period signal becomes a low level, the imaging element 11 terminates exposure for one frame and outputs serial data to the serial-parallel conversion unit 12 at high speed.
Then, as illustrated in FIG. 7(c), the data output from the imaging element 11 are written into the memory unit 13 via the serial-parallel conversion unit 12 at high speed.
On the other hand, as illustrated in FIG. 7(d), the data written into the memory unit 13 are sequentially output from the interface output processing unit 15 to the inspection device. However, because a transmission frame rate is slow, reading needs a time compared to writing.
When confirming that the inspection device acquires images for 50 frames, the object moving apparatus determines that this object has been completely captured and shifts to an operation for an object moving period to start to move the object.
Because the imaging device does not perform imaging until the next imaging start signal is input from the object moving apparatus, the imaging device does not perform imaging while the object is moving.
Then, when the movement of the object is completed, the next imaging start signal is input from the object moving apparatus and the next object is similarly captured as illustrated in FIG. 7(a).
As described above, because the conventional imaging device has the low transmission frame rate of the interface output processing unit 15 compared to the imaging frame rate of the imaging element 11 and the object moving apparatus cannot start to move the object until the reading of the set number of image data is completed, the entire inspection requires time and thus high throughput cannot be obtained.